Tamoxifen is a medication used to treat breast cancer and reduce the risk of recurrence for men and women. Tamoxifen also reduces the risk of getting breast cancer and is used as a preventative medicine for those at increased risk.
The Breast Cancer Prevention Trial studied healthy participants at increased risk of developing breast cancer and found that tamoxifen reduced the incidence of invasive breast cancer by 49 percent. A seven-year follow-up to the initial BCPT--"Current Status of the National Surgical Adjuvant Breast and Bowel Project P-1 Study," published in the Journal of the National Cancer Institute in November 2005--confirmed that tamoxifen reduced the risk of developing invasive breast cancer in healthy pre- and post-menopausal patients by nearly 50 percent.
As a treatment, tamoxifen is used with other measures, including surgery and chemotherapy.
Estrogen Receptors and Breast Cancer
Almost two-thirds of breast cancer tissue has receptors that are stimulated by estrogen and are referred to as Estrogen Receptor positive tumors. When estrogen binds to the breast tissue receptor, it sends a signal to the ductal cells to divide and grow. Healthy cells have mechanisms to control their growth. Cancer cells grow out of control because of mutations in their DNA, and in ER+ tumors, estrogen signals the cancer cells to grow.
Selective Estrogen Receptor Modulators
Tamoxifen is a Selective Estrogen Receptor Modulator. SERMs attach to estrogen receptors, which are located on cells throughout the body and either block or stimulate them. In breast tissue, tamoxifen attaches to the estrogen receptor and is inactive. It prevents circulating estrogen, which would stimulate the breast tissue to grow, from binding to the receptor. Tamoxifen is used after initial treatment of breast cancer. It prevents it from recurring in the same breast and from occurring in the healthy breast.
By binding to the estrogen receptor, tamoxifen keeps the receptor occupied and estrogen cannot attach to it and signal cell growth. Tamoxifen is inactive in breast tissue. Think of it as a baseball glove that already has a ball in it; the glove cannot catch another ball.
Length of Treatment
Tamoxifen is prescribed for five years in appropriate patients to treat ER+ tumors and as a prevention in high-risk patients. Studies are ongoing to see if there is any benefit to longer use. As with any medication, there are side effects and risks with tamoxifen. and these studies will help determine if the benefits of longer-term therapy outweigh the risks.
References
- National Cancer Institue Q & A Tamoxifen
- "Journal of the National Cancer Institute"; Tamoxifen for the prevention of breast cancer: Current status of the National Surgical Adjuvant Breast and Bowel Project P-1 Study; Fisher B, Costantino JP, Wickerham DL, et al; 2005; 97(22):1652--1662.
